阅读说明：本技术 一种热防护涂层及其制备方法 (Thermal protection coating and preparation method thereof ) 是由 郭嘉仪 田伟智 于 2020-12-31 设计创作，主要内容包括：本发明公开了一种热防护涂层及其制备方法,属于表面工程热喷涂技术领域,解决了现有的热防护涂层的有效防护时间较短,稳定性差的问题。所述热防护涂层包括自辐射层,自辐射层的制备原料包括La-2O-3和Cr-2O-3。热防护涂层的制备方法包括：根据质量配比称取La-2O-3粉末和Cr-2O-3粉末；将La-2O-3粉末和Cr-2O-3粉末放入球磨机中搅拌,混合均匀后进行高温烧结,随炉冷却至室温,获得混合粉末；将混合粉末、去离子水和粘结剂放入球磨机中搅拌混匀制备浆料；将浆料进行造粒,得到喷涂用粉体；干燥喷涂用粉体,然后将干燥后的喷涂用粉体装入送粉器中；采用等离子喷涂法在待喷涂基体试样表面喷涂粘结层；采用等离子喷涂法在粘结层表面喷涂自辐射层。本发明的热防护涂层热防护效果好。(The invention discloses a thermal protection coating and a preparation method thereof, belongs to the technical field of surface engineering thermal spraying, and solves the problems of short effective protection time and poor stability of the conventional thermal protection coating. The thermal protection coating comprises a self-radiation layer, and the preparation raw material of the self-radiation layer comprises La 2 O 3 And Cr 2 O 3 . The preparation method of the thermal protection coating comprises the following steps: weighing La according to mass ratio 2 O 3 Powder and Cr 2 O 3 Powder; la 2 O 3 Powder and Cr 2 O 3 Putting the powder into a ball mill, stirring, uniformly mixing, sintering at a high temperature, and cooling to room temperature along with the furnace to obtain mixed powder; putting the mixed powder, deionized water and a binder into a ball mill, and uniformly stirring to prepare slurry; granulating the slurry to obtain powder for sprayingA body; drying the powder for spraying, and then filling the dried powder for spraying into a powder feeder; spraying a bonding layer on the surface of a matrix sample to be sprayed by adopting a plasma spraying method; and spraying a self-radiation layer on the surface of the bonding layer by adopting a plasma spraying method. The thermal protection coating has good thermal protection effect.)

1. The thermal protection coating is characterized by comprising a self-radiation layer, wherein the preparation raw material of the self-radiation layer comprises La₂O₃And Cr₂O₃。

2. The thermal protection coating of claim 1, further comprising a bonding layer; the bonding layer is arranged between the self-radiation layer and the substrate.

3. The thermal protective coating of claim 1, wherein said La₂O₃And Cr₂O₃The mass ratio of (A) to (B) is 50-60: 40 to 50.

4. The thermal protective coating of claim 2 wherein the thickness of said bonding layer is greater than the thickness of said self-emissive layer.

5. A method of preparing a thermal protective coating, comprising:

step 1: weighing La according to mass ratio₂O₃Powder and Cr₂O₃Powder;

step 2: la₂O₃Powder and Cr₂O₃Putting the powder into a ball mill, stirring, uniformly mixing, putting into a crucible, sintering at high temperature, and cooling to room temperature along with a furnace to obtain mixed powder with a perovskite structure;

and step 3: putting the mixed powder, deionized water and a binder into a ball mill, and uniformly stirring to prepare slurry;

and 4, step 4: granulating the slurry to obtain powder for spraying;

and 5: drying the powder for spraying, and then filling the dried powder for spraying into a powder feeder;

step 6: spraying a bonding layer on the surface of a matrix sample to be sprayed by adopting a plasma spraying method;

and 7: spraying the powder for spraying prepared in the step 5 on the surface of the bonding layer by adopting a plasma spraying method to obtain a self-radiating layer; and finishing the preparation of the thermal protection coating.

6. The method of preparing a thermal protective coating according to claim 5, wherein said step 6 comprises:

step 601, clamping a substrate sample to be sprayed on a tool, starting a spraying system, and preheating the substrate after flame flow is stable;

and step 602, spraying a NiCoCrAlY metal layer as a bonding layer.

7. The preparation method of the thermal protection coating according to claim 5, wherein in the step 2, the sintering temperature is 1000-1200 ℃ and the sintering time is 3-5 h.

8. The method for preparing the thermal protection coating according to claim 5, wherein in the step 3, the mass of the binder is 3-5% of the mass of the mixed powder.

9. The method for preparing the thermal protective coating according to any one of claims 5 to 8, wherein in the step 6 and the step 7, the main gas is Ar and the auxiliary gas is H in the plasma spraying process₂The carrier gas is Ar.

10. The method for preparing a thermal protective coating according to any one of claims 5 to 9, wherein in step 6, during plasma spraying: the current is 500-600A, the main gas flow is 30-40 NLPM, the powder feeding speed is 3-5 r/min, and the spraying distance is 90-110 mm.

Technical Field

The invention belongs to the technical field of surface engineering thermal spraying, and particularly relates to a thermal protection coating and a preparation method thereof.

Background

With the rapid development of aerospace technology in China, the outer surface of the aerospace craft can be continuously exposed in a harsh pneumatic thermal environment during the high-speed long-time cruising and flying process of the aerospace craft, and in order to reduce the impact and high-temperature damage of the external high-temperature environment on the hot air flow of the parts in the product during the service process of the aerospace craft, ensure the normal work of the product, effectively improve the service life and the safety of the parts, the surface of the aerospace craft must be coated with a heat-proof material for external protection. The existing protective coating is usually of an anti-ablation type, the thermal protection effect is greatly reduced after the thermal balance is achieved for a certain time, and the problems of poor bonding force between the protective coating and a substrate, poor stability and easy falling are solved. Therefore, how to provide a protective coating with better thermal protection capability and better stability is a problem to be solved urgently.

Disclosure of Invention

In view of the above analysis, the present invention aims to provide a thermal protective coating and a method for preparing the same, which can solve at least one of the following technical problems: (1) the effective protection time of the existing thermal protection coating is short; (2) the existing thermal protection coating has poor stability.

The purpose of the invention is mainly realized by the following technical scheme:

in one aspect, the invention provides a thermal protective coating comprising a self-emissive layer prepared from a raw material comprising La₂O₃And Cr₂O₃。

Further, the thermal protective coating further comprises a bonding layer; the bonding layer is arranged between the self-radiation layer and the substrate.

Further, the La₂O₃And Cr₂O₃The mass ratio of (A) to (B) is 50-60: 40 to 50.

Further, the thickness of the bonding layer is larger than that of the self-radiation layer.

In another aspect, the present invention further provides a method for preparing a thermal protective coating, comprising:

step 1: weighing La according to mass ratio₂O₃Powder and Cr₂O₃Powder;

step 2: la₂O₃Powder and Cr₂O₃Putting the powder into a ball mill, stirring, uniformly mixing, putting into a crucible, sintering at high temperature, and cooling to room temperature along with a furnace to obtain mixed powder with a perovskite structure;

and step 3: putting the mixed powder, deionized water and a binder into a ball mill, and uniformly stirring to prepare slurry;

and 4, step 4: granulating the slurry to obtain powder for spraying;

and 5: drying the powder for spraying, and then filling the dried powder for spraying into a powder feeder;

step 6: spraying a bonding layer on the surface of a matrix sample to be sprayed by adopting a plasma spraying method;

and 7: spraying the powder for spraying prepared in the step 5 on the surface of the bonding layer by adopting a plasma spraying method to obtain a self-radiating layer; and finishing the preparation of the thermal protection coating.

Further, the step 6 comprises:

step 601, clamping a substrate sample to be sprayed on a tool, starting a spraying system, and preheating the substrate after flame flow is stable;

and step 602, spraying a NiCoCrAlY metal layer as a bonding layer.

Further, in the step 2, the sintering temperature is 1000-1200 ℃, and the sintering time is 3-5 hours.

Further, in the step 3, the mass of the binder is 3 to 5 percent of the mass of the mixed powder.

Further, in the step 6 and the step 7, in the plasma spraying process, the main gas is Ar, and the auxiliary gas is H₂The carrier gas is Ar.

Further, in the step 6, during the plasma spraying process: the current is 500-600A, the main gas flow is 30-40 NLPM, the powder feeding speed is 3-5 r/min, and the spraying distance is 90-110 mm.

Compared with the prior art, the invention can at least realize one of the following beneficial effects:

(1) the raw material for preparing the self-radiation layer of the thermal protection coating provided by the invention is La₂O₃And Cr₂O₃，La₂O₃And Cr₂O₃The structure has good radiation performance, and the structure can be used as a thermal protection coating to improve the thermal protection effect of the coating, for example, the emissivity of the thermal protection coating reaches 0.89, the thermal protection coating has higher emissivity, the stronger the capability of the thermal protection coating for radiating heat outwards, the more beneficial the heat in the environment can be transmitted back to the environment in a radiation mode, thereby reducing the temperature of the matrix and playing a role in thermal protection.

(2) According to the thermal protection coating provided by the invention, the metal layer is arranged between the substrate and the self-radiation layer to serve as the bonding layer, so that the thermal stress caused by the difference of thermal expansion coefficients is relieved, the stability of the thermal protection coating at high temperature is improved, and the finally prepared thermal protection coating has good thermal stability.

(3) The preparation method of the thermal protection coating provided by the invention adopts the plasma spraying process, and accurately controls the process parameters of the plasma spraying process such as main gas flow, current, powder feeding speed, spraying distance, spraying speed and the like, so that the prepared thermal protection coating has good surface quality, flat coating surface, no defects of cracks, layering, bubbling, stripping, looseness and the like, the porosity is less than 8%, the thermal protection coating has no defects of cracks, stripping and the like after being subjected to thermal shock for 10 times at 1200 ℃, the thermal stability is good, and the bonding strength between the coating and a matrix is more than 35 MPa. Can meet the use requirements of the aerospace craft.

Additional features and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and drawings.

Drawings

The drawings are only for purposes of illustrating particular embodiments and are not to be construed as limiting the invention.

FIG. 1 is an XRD phase pattern of the thermal protective coating of example 1;

FIG. 2 is a microstructure of the powder for spray coating of example 1, at a magnification of 250 times;

FIG. 3 is a microstructure morphology of the powder for spraying of example 1, magnified 1200 times;

fig. 4 is a photograph of the thermal protective coating of example 1.

Detailed Description

The preferred embodiments of the present invention are described in detail below.

In the process of high-speed long-time cruising flight of the aerospace craft, the outer surface of the aerospace craft can be continuously exposed in a harsh pneumatic thermal environment, and in order to reduce the impact and high-temperature damage of the external high-temperature environment of the aerospace craft on the hot air flow of the parts in the product in the service process, ensure the normal work of the product, effectively improve the service life and the safety of the parts, the surface of the aerospace craft must be coated with a heat-proof material for external protection. The existing protective coating is usually of an anti-ablation type, the thermal protection effect is greatly reduced after the thermal balance is achieved for a certain time, and the problems of poor bonding force between the protective coating and a substrate, poor stability and easy falling are solved. Therefore, it is desirable to provide a thermal protective coating with better thermal protection capability and stability.

The invention provides a thermal protection coating, which comprises a self-radiation layer, wherein the preparation raw material of the self-radiation layer comprises La₂O₃And Cr₂O₃。

Considering that the thermal protection coating is mainly applied to the surface of an aircraft, the material of the substrate on the surface of the aircraft is metal, if a ceramic self-radiation layer is directly sprayed on the surface of the metal substrate, the difference of the thermal expansion coefficients between the self-radiation layer and the substrate is large, and the coating is easy to crack and peel under the action of thermal stress. Therefore, in order to reduce the thermal stress between the self-radiating layer and the substrate and improve the stability of the thermal protection coating, the thermal protection coating also comprises a bonding layer; the bonding layer is arranged between the self-radiating layer and the substrate. The adhesive layer may be a metal layer.

Specifically, the bonding layer is a NiCoCrAlY metal layer.

The invention provides a preparation method of the thermal protection coating, which comprises the following steps:

step 1: weighing La according to mass ratio₂O₃Powder and Cr₂O₃Powder;

step 2: la₂O₃Powder and Cr₂O₃Putting the powder into a planetary ball mill, stirring, uniformly mixing, putting into a crucible, sintering at high temperature, and cooling to room temperature along with a furnace to obtain mixed powder with a perovskite structure;

and step 3: putting the mixed powder, deionized water and a binder into a ball mill, and uniformly stirring to prepare slurry;

and 4, step 4: feeding the slurry into a spray drying tower for granulation to obtain powder for spraying;

and 5: drying the powder for spraying, and then filling the dried powder for spraying into a powder feeder;

step 6: spraying a NiCoCrAlY metal layer on the surface of a matrix sample to be sprayed by adopting a plasma spraying method to serve as a bonding layer;

and 7: spraying the powder for spraying prepared in the step 5 on the surface of the bonding layer by adopting a plasma spraying method to obtain a self-radiating layer; and finishing the preparation of the thermal protection coating.

In step 1, La is added₂O₃And Cr₂O₃The composite structure has a similar crystal structure and is an oxide with a similar structure, the composite structure with the perovskite structure can be better synthesized through solid-phase reaction, the structure has good radiation performance, and the thermal protection effect of the coating can be improved by taking the structure as a thermal protection coating. Considering La₂O₃Powder and Cr₂O₃An excessive mass ratio of the powders may result in excessive La in the resultant mixed powder₂O₃(ii) a Too low a mass ratio results in excessive Cr in the resultant mixed powder₂O₃. Therefore, to ensure that the two powders react sufficiently, La is controlled₂O₃Powder and Cr₂O₃The mass ratio of the powder is 50-60: 40 to 50.

In particular toIn the above step 1, La₂O₃Powder and Cr₂O₃An excessively large particle size of the powder may result in insufficient reaction of the two powders. Thus, controlling La₂O₃Powder and Cr₂O₃The particle size of the powder is 1-5 μm.

Specifically, in the step 2, the sintering temperature is too low, and La is formed₂O₃Powder and Cr₂O₃The powder does not react; the sintering temperature is too high, which causes the crystal grains to grow and destroys the structure of the finally synthesized mixed powder. Therefore, the sintering temperature is controlled to be 1000-1200 ℃, and the sintering time is controlled to be 3-5 h.

Specifically, in the step 2, the particle size of the mixed powder is 1-5 μm.

Specifically, in the step 3, the mass of the mixed powder is controlled to be 30-40% of the total mass of the mixed powder, the deionized water and the binder.

Specifically, in the step 3, the content of the binder is too high, so that the later granulation of the mixed powder is influenced, and a stable spherical structure is not easily formed; the content is too low to sufficiently bind the mixed powder. Therefore, the mass of the binder is controlled to be 3% to 5% of the mass of the mixed powder.

Specifically, in step 3, the binder is polyvinyl alcohol.

Specifically, in the step 4, the slurry is sent into a spray drying tower for granulation to obtain powder for spraying, and the powder for spraying has an excessively large particle size, which leads to insufficient melting in the subsequent plasma spraying process, and a gun blockage phenomenon is easily caused by an excessively small particle size. Therefore, the particle size of the powder for spraying is controlled to be 15 to 90 μm.

Specifically, in the step 4, in order to fully evaporate the water in the slurry, the temperature of an air inlet of the spray drying tower is 200-250 ℃, and the temperature of an air outlet is 100-110 ℃; in order to ensure that the particle size of the powder obtained after granulation is 15-90 μm, the frequency of a peristaltic pump is controlled to be 30-40 Hz (such as 35Hz) and the frequency of an atomizing disc is controlled to be 25-35 Hz (such as 30Hz) in the granulation process.

Specifically, the step of drying the powder for spraying in step 5 is: and putting the powder for spraying into a clean tray, and then drying in an oven at 100-120 ℃ for 2-4 h.

Specifically, the step 6 specifically includes the following steps:

step 601, clamping a sample of a substrate to be sprayed (such as a stainless steel substrate) on a tool, starting a spraying system, and preheating the substrate for 1 time after flame flow is stable; preheating the substrate can increase the temperature of the substrate surface, thereby reducing the thermal stress between the bonding layer and the substrate;

and step 602, spraying a NiCoCrAlY metal layer as a bonding layer.

Specifically, in the step 6 and the step 7, in the plasma spraying process, the main gas is Ar, and the auxiliary gas is H₂The carrier gas is Ar.

Considering that in the above steps 6 and 7, the main gas flow can change the main arc gas flow and the form of the gas distribution ring, change the gas flow direction and flow velocity, change the compression to the arc, change the ionization degree, temperature, current density and the like of the plasma arc column region, improve the main gas flow in a certain range, improve the particle speed and improve the particle temperature; however, for a given lance and current, increasing the main gas flow beyond a certain value will result in a drop in the temperature of the particles. The addition of the auxiliary gas can improve the efficiency of transferring heat from the plasma jet to the powder, but can also improve the viscosity of the jet to accelerate the speed of the powder, so that the time of the powder in the plasma flame flow is reduced, therefore, when the flow of the auxiliary gas is proper, the speed of the powder can be improved, the temperature of the powder can be improved, and when the flow is too high, the melting degree of the powder is reduced, so that the pores of a coating are increased, and the performance is reduced. The spraying material has high melting point and large specific heat, requires a coating layer to have higher compactness, and selects larger current under the condition of small change of other parameters. The powder feeding rate mainly affects the deposition rate and porosity of the coating, and when the powder feeding rate is lower, the temperature of the sprayed particles is reduced along with the increase of the powder feeding rate, but the deposition rate of the coating is increased along with the increase of the powder feeding rate; when the powder feeding rate is increased to a certain degree, the porosity inside the coating layer is sharply increased due to the decrease in the melting degree of the powder. Therefore, the spraying process parameters in the above steps 6 and 7 are controlled as shown in the following table 1:

TABLE 1 spray coating Process parameters

Parameters of spraying	Self-radiating layer	Adhesive layer
			Current (A)	500～600	500～600
Main air flow (NLPM)	30～40	30～40
			Powder feeding speed (r/min)	8～12	3～5
Spraying distance (mm)	90～110	90～110
			Spraying speed (mm/s)	500～600	500～600
Auxiliary air flow (NLPM)	5～10	1～6
			Carrier gas flow (NLP)M)	1～3	2～4

Specifically, in the above steps 6 and 7, the thickness of the bonding layer is greater than that of the self-radiating layer, because the thicker bonding layer enables the coating to have better stability, and on the other hand, the self-radiating layer is a functional layer, and the effect of radiating heat can be realized without too much thickness. Illustratively, the thickness of the bonding layer is 0.06-0.10 mm, and the thickness of the self-radiation layer is 0.01-0.05 mm.

Specifically, in the step 7, the emissivity of the thermal protection coating reaches 0.89, the porosity is less than 8%, the coating has no defects of cracks, peeling and the like after being subjected to thermal shock for 10 times at 1200 ℃, the thermal stability is good, and the bonding strength between the coating and the matrix is more than 35 MPa. The emissivity of the thermal protection coating is higher, and the ability of the thermal protection coating to radiate heat outwards is stronger, so that the thermal protection coating is more favorable for transferring the heat in the environment back to the environment in a radiation mode, thereby reducing the temperature of the substrate and playing a role in thermal protection.

Compared with the prior art, the thermal protection coating provided by the invention has the advantages that the metal layer is arranged between the substrate and the self-radiation layer as the bonding layer, so that the thermal stress caused by the difference of thermal expansion coefficients is relieved, the stability of the thermal protection coating at high temperature is improved, and the finally prepared thermal protection coating has good thermal stability.

The raw material for preparing the self-radiation layer of the thermal protection coating provided by the invention is La₂O₃And Cr₂O₃，La₂O₃And Cr₂O₃The composite structure has a similar crystal structure and is an oxide with a similar structure, the composite structure with the perovskite structure can be better synthesized through solid-phase reaction, the structure has good radiation performance, and the thermal protection effect of the coating can be improved by taking the structure as a thermal protection coating (the emissivity of the thermal protection coating reaches 0.89).

The preparation method of the thermal protection coating provided by the invention adopts the plasma spraying process, and accurately controls the process parameters of the plasma spraying process such as main gas flow, current, powder feeding speed, spraying distance, spraying speed and the like, so that the prepared thermal protection coating has good surface quality, flat coating surface, no defects of cracks, layering, bubbling, stripping, looseness and the like, the porosity is less than 8%, the thermal protection coating has no defects of cracks, stripping and the like after being subjected to thermal shock for 10 times at 1200 ℃, the thermal stability is good, and the bonding strength between the coating and a matrix is more than 35 MPa. Can meet the use requirements of the aerospace craft.

Example 1

The embodiment provides a thermal protection coating, and a preparation method of the thermal protection coating comprises the following steps:

step 1: weighing La according to mass ratio₂O₃Powder and Cr₂O₃Powder; wherein La₂O₃Powder and Cr₂O₃The mass ratio of the powder is 60: 40;

step 2: la₂O₃Powder and Cr₂O₃Putting the powder into a planetary ball mill, stirring, uniformly mixing, putting into a crucible, sintering at high temperature, and cooling to room temperature along with a furnace to obtain mixed powder with a perovskite structure; wherein the high-temperature sintering temperature is 1100 ℃, and the sintering time is 3 h;

and step 3: putting the mixed powder, deionized water and a binder into a ball mill, and uniformly stirring to prepare slurry; wherein the mass of the mixed powder accounts for 35% of the total mass of the mixed powder, the deionized water and the binder, and the mass of the binder is 3% of the mass of the mixed powder;

and 4, step 4: feeding the slurry into a spray drying tower for granulation to obtain powder for spraying; wherein the temperature of an air inlet of the spray drying tower is 200 ℃, the temperature of an air outlet is 110 ℃, the frequency of a peristaltic pump is 35Hz, and the frequency of an atomizing disc is 30 Hz;

and 5: drying the powder for spraying (drying in an oven at 100 ℃ for 2h), and then putting the dried powder for spraying into a powder feeder;

step 6: clamping a sample of a stainless steel substrate to be sprayed on a tool, starting a plasma spraying system, preheating the substrate for 1 time after flame flow is stabilized, and spraying a NiCoCrAlY metal layer as a bonding layer; the thickness of the bonding layer is 0.06 mm;

and 7: spraying the powder for spraying prepared in the step 5 on the surface of the bonding layer by adopting a plasma spraying method to obtain a self-radiating layer; the thickness of the self-radiation layer is 0.05 mm; and finishing the preparation of the thermal protection coating.

Wherein in the above step 6 and step 7, the main gas is Ar and the auxiliary gas is H₂The carrier gas is Ar. The spraying process parameters in the above steps 6 and 7 are shown in the following table 2:

TABLE 2 spray coating Process parameters

Parameters of spraying	Self-radiating layer	Adhesive layer
			Current (A)	500	500
Main air flow (NLPM)	30	40
			Powder feeding speed (r/min)	8	5
Spraying distance (mm)	90	90
			Spraying speed (mm/s)	500	500
Auxiliary air flow (NLPM)	5	1
			Carrier gas flow (NLPM)	3	2

The microscopic morphology of the interior of the coating was observed using a scanning electron microscope and the coating phase was characterized by XRD with the results shown in figures 1 to 3. FIG. 1 is an XRD phase diagram of a thermal protective coating, and FIGS. 2 and 3 are microstructure morphology diagrams of powder for spraying; FIG. 4 is a photograph of the thermal protective coating of example 1, showing no surface abnormality and good appearance.

Example 2

The embodiment provides a thermal protection coating, the preparation method of the thermal protection coating is the same as that of the embodiment 1, and the specific process parameters are as follows:

step 1: la₂O₃Powder and Cr₂O₃The mass ratio of the powder is 50: 50;

step 2: the high-temperature sintering temperature is 1100 ℃, and the sintering time is 4 h;

and step 3: the mass of the mixed powder accounts for 35% of the total mass of the mixed powder, the deionized water and the binder, and the mass of the binder is 4% of the mass of the mixed powder;

and 4, step 4: the temperature of an air inlet of the spray drying tower is 200 ℃, the temperature of an air outlet is 110 ℃, the frequency of a peristaltic pump is 35Hz, and the frequency of an atomizing disc is 30 Hz;

and 5: drying in an oven at 100 ℃ for 2 h;

step 6: the thickness of the bonding layer is 0.07 mm;

and 7: the thickness of the self-radiating layer was 0.04 mm.

The spraying process parameters in the above steps 6 and 7 are shown in the following table 3:

TABLE 3 spray coating Process parameters

Parameters of spraying	Self-radiating layer	Adhesive layer
			Current (A)	550	600
Main air flow (NLPM)	35	35
			Powder feeding speed (r/min)	9	4
Spraying distance (mm)	100	100
			Spraying speed (mm/s)	550	550
Auxiliary air flow (NLPM)	7	3
			Carrier gas flow (NLPM)	2	3

Example 3

The embodiment provides a thermal protection coating, the preparation method of the thermal protection coating is the same as that of the embodiment 1, and the specific process parameters are as follows:

step 1: la₂O₃Powder and Cr₂O₃The mass ratio of the powder is 55: 45;

step 2: the high-temperature sintering temperature is 1100 ℃, and the sintering time is 3 h;

and step 3: the mass of the mixed powder accounts for 40% of the total mass of the mixed powder, the deionized water and the binder, and the mass of the binder is 3% of the mass of the mixed powder;

and 4, step 4: the temperature of an air inlet of the spray drying tower is 200 ℃, the temperature of an air outlet is 110 ℃, the frequency of a peristaltic pump is 35Hz, and the frequency of an atomizing disc is 30 Hz;

and 5: drying in an oven at 100 ℃ for 2 h;

step 6: the thickness of the bonding layer is 0.1 mm;

and 7: the thickness of the self-radiating layer was 0.01 mm.

The spraying process parameters in the above steps 6 and 7 are shown in the following table 4:

TABLE 4 spray coating Process parameters

Parameters of spraying	Self-radiating layer	Adhesive layer
			Current (A)	580	520
Main air flow (NLPM)	35	30
			Powder feeding speed (r/min)	12	5
Spraying distance (mm)	110	110
			Spraying speed (mm/s)	600	600
Auxiliary air flow (NLPM)	10	6
			Carrier gas flow (NLPM)	3	4

Example 4

The embodiment provides a thermal protection coating, the preparation method of the thermal protection coating is the same as that of the embodiment 1, and the specific process parameters are as follows:

step 1: la₂O₃Powder and Cr₂O₃The mass ratio of the powder is 50: 45;

step 2: the high-temperature sintering temperature is 1100 ℃, and the sintering time is 3 h;

and step 3: the mass of the mixed powder accounts for 35% of the total mass of the mixed powder, the deionized water and the binder, and the mass of the binder is 3% of the mass of the mixed powder;

and 4, step 4: the temperature of an air inlet of the spray drying tower is 200 ℃, the temperature of an air outlet is 110 ℃, the frequency of a peristaltic pump is 35Hz, and the frequency of an atomizing disc is 30 Hz;

and 5: drying in an oven at 100 ℃ for 2 h;

step 6: the thickness of the bonding layer is 0.09 mm;

and 7: the thickness of the self-radiating layer was 0.02 mm.

The spraying process parameters in the above steps 6 and 7 are shown in the following table 5:

TABLE 5 spray coating Process parameters

Parameters of spraying	Self-radiating layer	Adhesive layer
			Current (A)	560	510
Main air flow (NLPM)	33	30
			Powder feeding speed (r/min)	10	4
Spraying distance (mm)	100	100
			Spraying speed (mm/s)	600	600
Auxiliary air flow (NLPM)	8	4
			Carrier gas flow (NLPM)	2	3

Comparative example 1

The spray coating process parameters of this comparative example 1 were the same as example 1 except that the thickness of the adhesive layer was 0.02mm and the thickness of the self-radiating layer was 0.08 mm.

The surface quality and performance results for the thermal protective coatings prepared in examples 1-4 and comparative example 1 are shown in table 6 below.

TABLE 6 surface quality and Properties of the coatings of examples 1-4 and comparative example 1

The comparison table 6 shows that the thermal protection coating has high bonding strength with a substrate test piece, high emissivity and good stability at high temperature, can transfer heat to the environment in a radiation mode, and plays a long-time effective thermal protection role on the substrate.

The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are included in the scope of the present invention.